Anaerobic digestion is a collection of processes wherein bacteria breakdown organic biomass without the presence of oxygen. Examples of resulting products of anaerobic digestion are methane and carbon dioxide. These biogas products can be used directly for fuel, e.g. in heat and power gas engines, or converted to other forms of renewable energy, e.g. natural gas.
The process of anaerobic digestion typically begins with bacterial hydrolysis of the input materials. Insoluble organic polymers, e.g. carbohydrates, are broken down to soluble derivatives that become available for other bacteria. Acidogenic bacteria then convert the soluble derivatives, e.g. sugars and amino acids, into carbon dioxide, hydrogen, ammonia, and short chain fatty acids (also known as “volatile fatty acids” or VFA). Finally, methanogenic bacteria, or methanogens, convert the VFA to methane and carbon dioxide. In some processes, an intermediate step called acetogenesis occurs where the acidogenic bacteria convert VFAs into acetic acid, which the methanogens utilize in the production of methane and carbon dioxide.
The breakdown of complex polymers during anaerobic digestion is typically slow and inefficient with typical values for the conversion of the volatile solids, which are the main reservoir of these compounds, within the range of 0.1% to 10% of the total amount of available solids. In addition, the ecosystem of the bacterial milieu can be very fragile and sensitive to changes in feedstock and to the surrounding bacterial environment. Thus, there exists a need for improved methods and processes for facilitating anaerobic digestion and increasing the efficiency and resiliency of such processes.